This invention relates to connecting or coupling two adjacent reinforced precast concrete modules or sections or members together, and more specifically, for joining or coupling parallel spaced elongated reinforcing bars, commonly referred to as rebars, in one precast concrete member with corresponding and axially aligned reinforcing bars or rebars in adjacent precast concrete members. The reinforced precast concrete members may be in various forms, for example, in the form of precast concrete vertical column sections, such as disclosed in U.S. Pat. No. 4,196,557 and in European Patent No. 1,561,874 or in the form of precast vertical wall panels or sections.
In the construction of vertical walls from precast concrete wall panels or sections, it is common for the vertical rebars in each section to have exposed upper end portions projecting from the top edge surface of the section, and the lower portion of each section to have embedded tubular metal couplers. The couplers are attached to the lower end portions of the vertical reinforcing bars in the section and receive the upwardly projecting end portions of the vertically aligned reinforcing bars in the adjacent lower section. The tubular couplers are then pumped full of a grout mixture which sets up and couples the vertically aligned rebars together, for example, as disclosed in UK patent application No. 2,034,857 and in U.S. Pat. No. 5,383,740 and U.S. Pat. No. 5,974,761 and in Japanese patent application No. 2005-264600.
This grout-type of rebar connector or coupling is used for joining or connecting precast wall panels or sections which may be match-cast at a precast plant and are stacked at a construction site to form a vertical wall. In the match-cast method, sometimes alternate wall panels or sections are cast on a horizontal floor or bed surface between forms and with each panel having steel wire reinforcing mats and parallel spaced rebars. The rebars have end portions projecting from one edge surface of the panel and opposite end portions connected to grout-type tubular couplers adjacent the opposite edge surface of the wall panel. After the poured concrete in the alternate wall panels or sections cures, the forms are removed, and parallel rebars with attached tubular couplers are assembled between the opposing edge surfaces of the alternate concrete wall sections along with steel reinforcing grids or mats. The opposing edge surfaces of the alternate concrete wall sections are sprayed with a release agent, and the intermediate concrete wall section is then cast with concrete.
After the concrete forming all of the intermediate wall sections cures, the outer forms are removed and the match-cast sections are separated, ready to be placed in storage or transported to the construction site. After the wall sections arrive at the construction site, the sections are successively stacked with the aid of a crane to form a vertical wall. The embedded tubular rebar couplers in the lower portion of each wall section receive the upwardly projecting end portions of the corresponding vertically aligned rebars in the adjacent lower section. The couplers are then pumped full of grout for connecting the opposing end portions of the vertical rebars together, for example, as shown in the above-mentioned Japanese patent application.
The use of the grout-filled rebar couplers has disadvantages in that the grout requires several hours to cure and to develop a minimum tensile strength, and the vertically stacked wall sections usually require bracing until the grout cures. In addition, the grout-filled couplers can not be used at a construction site when the ambient temperature is low unless the wall receives a cover and the wall is heated under the cover. The grout-filled couplers also require significant time to fill, and there is no positive assurance that each coupler has been completely filled or that the grout has cured properly to provide the required coupling strength for the vertically aligned connected rebars. Typically, the compressive strength of field mixed grout must be determined by performing compressive tests on cubes of cured material at prescribed intervals. It can take one week for results to be known and for grout strength to be validated. The grout is also subject to shrinkage over a period of time, and this can result in weakening the splice or connection of the rebars.
It is also known to form precast concrete wall panels or sections or modules having embedded steel anchor plates connected by welds to the reinforcing bars within the sections or modules. After the concrete cures, and the modules are delivered to a construction site where the modules are stacked vertically with the use of an erection crane, the stacked modules are shimmed so that they are horizontal, and adjacent anchor plates are welded together to maintain panel alignment, sometimes with a separate weld plate. However, the welding requires special welding equipment at the construction site which adds significantly to the construction or erection costs, and sometimes the welds require certified welders and validation by ongoing tests and quality checks.
Other forms of connecting adjacent precast concrete wall panels or modules or sections use tie bolts which connect adjacent surface anchor plates welded to corresponding reinforcing rods or bars within the concrete sections, for example, as disclosed as U.S. Pat. No. 4,781,006. However, welding anchor plates to rebars is not desirable since it is difficult to determine if the welds produce acceptable connections. Another form of connecting precast concrete panels or members with threaded fasteners or bolts, is disclosed in U.S. Pat. No. 6,058,672. In this patent, U-shaped anchor members surround the reinforcing bars within one concrete member and have threaded tubular fittings for receiving threaded fasteners or bolts. The bolts extend through U-shaped brackets embedded within a second concrete member and have holes receiving reinforcing rods.